1. Field of the Invention
The present invention relates to semiconductor carbon nanotubes functionalized by hydrogen, and more particularly, to a method for fabricating the same.
2. Description of the Related Art
Carbon nanotubes are cylindrical or tubular forms of carbon having diameters ranging from a few to tens of nanometers and lengths of tens of micrometers.
FIG. 1 illustrates the configuration of a conventional carbon nanotube. Carbon nanotubes may be thought of as being formed by rolling up sheets of graphite (a hexagonal lattice of carbon) into cylinders. The unique properties of carbon tubes are determined by the length, configuration and diameter of the carbon tubes as determined by the angle at which a sheet of graphite being rolled is twisted, i.e., chirality, and the diameter of the carbon nanotubes at the initial stage of rolling.
Referring to FIG. 1, vector {right arrow over (C)}h from an arbitrary start point A to an end point A′, which meet when the sheet is rolled up, is shown. If it is assumed that A has coordinates (0, 0) and A′ has coordinates (n, m), then vector {right arrow over (C)}h can be expressed with unit vectors {right arrow over (a)}1 and {right arrow over (a)}2 as in equation (1) below.{right arrow over (C)}h=n{right arrow over (a)}1+m{right arrow over (a)}2  (1)
The diameter dt of the carbon nanotube can be calculated using equation (2) below.
                              d          t                =                              0.246            ⁢                                          (                                                      n                    2                                    +                                      n                    ⁢                                                                                  ⁢                    m                                    +                                      m                    2                                                  )                                            1                /                2                                              π                                    (        2        )            
Carbon nanotubes feature very high aspect ratios of 1,000 or greater and have the electrical properties of a metal or of a semiconductor depending on their diameters and configurations. Metallic carbon nanotubes are known to have high electrical conductance.
FIG. 2A illustrates a special type of a carbon nantotube in zigzag form, which is obtained when m=0. FIG. 2B illustrates a carbon nanotube having an armchair configuration, which is obtained when n=m.
Most carbon nanotubes have chiral configurations spirally arranged along arbitrary tubular axes. Carbon nanotubes formed from a single sheet of graphite rolled up into a cylinder are called “single wall nanotubes” (SWNT), and carbon nanotubes formed from multiple sheets of graphite rolled up into cylinders inside other cylinders are called “multi-wall nanotubes” (MWNT).
Conventionally, carbon nanotubes are manufactured using arc discharging, laser ablation, chemical vapor deposition (CVD), and like processes. Such conventional techniques, however, cannot control chirality, and lead to a mixture of metallic and semiconductor carbon nanotube particles, which cannot be used to manufacture metallic nanotransistors. In addition, transistors manufactured from semiconductor carbon nanotubes do not work at an ambient temperature due to the small energy bandgap of the semiconductor carbon nanotubes.
To overcome such drawbacks, a method has been developed for converting metallic carbon nanotubes into semiconductor carbon nanotubes by separating outer walls of MWNTs to reduce the diameter of the carbon nanotubes. However, this method involves placing the metallic carbon nanotubes in contact with an electrode and applying a high current to them, which renders the overall process to be complex. In addition, the method can be applied neither directly to transistors nor to SWNTs having no extra wall to be separated out.
Another conventional method for converting semiconductor carbon nanotubes into metallic carbon nanotubes by the addition of alkali metal has been suggested. However, this method cannot be applied to convert metallic carbon nanotubes into semiconductor carbon nanotubes nor to convert narrow bandgap semiconductor carbon nanotubes into large bandgap semiconductor carbon nanotubes.